More than a hundred firefighters battled on Monday a massive fire inside a Soviet-era chemical plant in Yerevan that has largely stood idle for the last several years.

The fire broke out at the Nairit plant located on the city’s southern outskirts in the morning for reasons that were not immediately clear. It engulfed storage tanks filled with combustible chemical waste. Thick black smoke billowed skyward throughout the day, with firefighting crews struggling to contain the blaze which still raged as of 9 pm local time.

The Armenian Ministry of Emergency Situations said late in the evening that the fire is now “under the full control of the firefighters” and will not spread to other parts of Nairit.

“Nobody was hurt,” the chief of the ministry’s Rescue Service, Mushegh Ghazarian, told reporters at the scene earlier in the day. “We are cooling the site to prevent the spread of the fire.”

Three firefighters were intoxicated with the smoke and required medical assistance.

Emergency services refrained from evacuating residents of nearby residential areas, insisting that the smoke emitted by the burning waste is not hazardous. Ghazarian said only that they should keep their windows closed.

The Armenian Ministry of Health seemed more worried, however, urging local residents -- especially children and individuals suffering from respiratory problems -- to avoid staying outdoors for long.

The burning chemical waste is a type of varnish generated as a result of the production of synthetic rubber, Nairit’s main product. It already caused a similar fire in 2009.

“We used to burn and even sell this substance in small quantities when the plant was operational” Nairit’s former executive director, Karen Israelian, told RFE/RL’s Armenian service (Azatutyun.am). “It doesn’t damage the plant, but you can’t dispose of it.”

The chemical giant, which used to employ several thousand people, struggled to remain afloat after the collapse of the Soviet Union, repeatedly changing foreign owners and operators in murky deals overseen by successive Armenian governments.

Nairit has had only 250 or so employees since 1,700 of its remaining workers were laid off in January 2016. In November, a Yerevan court declared the company bankrupt because of its failure to pay electricity bills totaling $2.6 million.